Hithereto, apparatuses of this kind have been known, as typically described in, for example, Japanese Utility Model Publication No. 50-35513, which teaches a hoisting device for an automatic warehousing crane. In this prior art arrangement, the automatic warehousing crane comprises an upper structure having guide rollers, a travelling lower structure, an upward and downward movable transfer carriage, a control board, a drive mechanism, and a hoisting device body for driving the upward and downward movable transfer carriage.
The hoisting device body includes an electric motor mounted on a frame, an upper rope pulley carried by the frame at a midportion thereof and geared to the electric motor, and a pair of lower rope pulleys, right and left, carried by the frame at a level lower than the upper rope pulley, the upper rope pulley and the pair of lower rope pulleys being interlockingly connected by gears.
For wire run, the arrangement in this prior art is such that two wire ropes put on the upper rope pulley are extended downward to engage the two lower rope pulleys from the inner side and are then turned outward to extend upward until they engage a sheave which in turn guide the pair of ropes downward, the pair of ropes being connected at one end to a counterweight via an equalizer, the other ends of the ropes being connected to the upward and downward movable transfer carriage in a longitudinally spaced apart relation.
In this proir art arrangement, the upper rope pulley is driven forward or reverse by the motor to rotate the two lower rope pulleys in a same direction thereby to move the wire ropes forward or reverse for upward or downward movement of the upward and downward movable transfer carriage. The use of wire ropes is intended to provide for weight reduction as compared with the use of chains to enable the use of an electric motor of a smaller capacity, and to decrease noise.
According to the above described arrangement of the prior art apparatus, a load applied to both ends of each wire rope acts toward relaxing wire rope winding about the rope pulley, that is, toward relieving frictional force on the rope pulley. Therefore, the wire ropes cannot have sufficient moving force applied thereto.
This prior art arrangement, which includes a pair of lower rope pulleys and gears, involves a relatively large number of parts and is rather complicated. As such, in some situation, the crane may be too large in width to enter the path for its run. Further, since the rope pulleys have their respective shafts supported at both ends on a box-like frame, it is rather difficult to pass the wire rope between the rope pulleys in the stage of assembly work.
Another problem relates to the fact that there is provided only one counterweight. When a larger-size (or heavier) counterweight is employed so as to reduce the capacity of the electric motor, the counterweight, normally disposed within a post, has an increased height and, accordingly, a stroke of counterweight movement, or a stroke of vertical movement of the upward and downward movable transfer carriage, is made shorter.
The fact that the electric motor, heavy in weight, is mounted on the frame results in the drive portion being tall in height, which means that the drive portion is positionally unstable. Further, mounting of the motor at such a high location is inconvenient from the standpoints of wiring work and maintenance.
Another problem is that the direction of wire rope winding about the upper rope pulley is opposite to the direction of wire winding about the lower rope pulleys. This means that bending force acts on the wire ropes alternately in opposite directions, which results in decreasing the service life of the wire ropes.
The counterweight, located externally of the upper structure, is liable to run out as it is moved upward and downward. Provision of guide means for the counterweight may add to the complicatedness of the arrangement.
When the wires have been stretched in course of use, the stretch will easily affect the transfer carriage in such a way as to tilt the transfer carriage. Such wire stretching must be adjusted at wire ends by operating an equalizer, but it is no easy job to effect such adjustment.
As another arrangement of the type has been proposed a travelling crane for warehousing use as typically described in Japanese Laid-Open Patent Application No. 2-182604. This prior art crane comprises a lower frame, a horizontal run drive unit and a vertical run drive unit arranged on one-end side of the lower frame as viewed in the direction of movement thereof (or on the outer position side), a pair of support posts extending upward from the lower frame, an upward and downward movable carriage mounted between the support posts, and a box-like crane control unit provided on the other end side of the lower frame as viewed in the direction of movement thereof (on the home position side).
The horizontal run drive unit comprises a frame member mounted to one lower end of the lower frame, a drive wheel carried by the frame member, and a reduction gear and a braked motor, both geared to the drive wheel, which are mounted on one side of the frame member as viewed widthwise of the crane.
The vertical run drive unit comprises a frame member mounted to one upper end of the lower frame, a toothed drive wheel carried by the frame member and having its shaft supported on both sides, a motor located above the toothed drive wheel and geared to the shaft via a reduction gear located on the other side of the crane widthwise thereof, and a chain held in engagement with the toothed drive wheel and interlockingly connected to the upward and downward movable carriage. In this prior art arrangement, by motor-driving the toothed drive wheel forward and reverse it is possible to drive the chain forward and reverse thereby to move the carriage upward and downward.
According to the above described arrangement of the prior art crane, the shaft on which the toothed drive wheel is mounted is supported on a frame member. This makes it difficult to pass the chain beneath the toothed drive chain at the stage of assembly work. That also makes it difficult to perform maintenance and inspection. Another problem is that a crane control unit for controlling the horizontal and vertical run drive units is disposed at a location most remote from those units. This makes it difficult to carry out wiring arrangement between the control unit and the drive units. Further, the toothed drive wheel is exposed at sides and top thereof. This poses a problem from the standpoint of safety, because other objects or an operator may have a chance of easy contact with them.